EFFECTS OF PISTACHIOS AS A NIGHTTIME SNACK COMPARED TO EDUCATION TO CONSUME 1-2 CARBOHYDRATE EXCHANGES ON GLYCEMIC CONTROL, CARDIOVASCULAR DISEASE RISK FACTORS, AND THE GUT MICROBIOTA IN ADULTS WITH PREDIABETES
Open Access
- Author:
- Riley, Terrence
- Graduate Program:
- Nutritional Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 14, 2023
- Committee Members:
- Meg Bruening, Program Head/Chair
Penny Kris-Etherton, Chair & Dissertation Advisor
Gregory Shearer, Major Field Member
Kristina Petersen, Special Member
Vishal Singh, Outside Field Member
Michael Russell, Outside Unit Member - Keywords:
- Chronic Disease
Prediabetes
Pistachio
Fasting Plasma Glucose
Lipids
Lipoproteins
Vascular Health
Gut Microbiota
Nighttime Snack - Abstract:
- The aim of this dissertation was to investigate the glycemic, cardiometabolic, and gut microbial effects of consuming pistachios as a nighttime snack, compared to education to consume a 1-2 carbohydrate (CHO) exchanges (usual care: 15-30 g CHO), in adults with prediabetes. We conducted a randomized 2-period crossover trial with 12-week intervention periods and > 4-week washout. The conditions were 57 g unsalted, pistachios [324 kcal (fat 26 g; CHO 16.04 g; protein 11.9 g; saturated fat: 3.2 g; monounsaturated fat: 13.9 g; polyunsaturated fat: 7.54 g; fiber: g; sodium: 3.4 mg)] and education to consume 1-2 CHO exchanges (15-30 g CHO). Participants were instructed to consume the study foods after dinner, before bedtime, and consume no other calorie-containing food or drinks after the snack. Additionally, participants were instructed to avoid consuming any other pistachios, peanuts, or tree nuts for the duration of the study. The primary outcome was fasting plasma glucose (FPG) and secondary outcomes were insulin, hemoglobin A1c (HbA1c), insulin resistance (Homeostatic model assessment of insulin resistance [HOMA-IR]), lipids/lipoproteins, brachial blood pressure (BP), central BP, measures of arterial stiffness (pulse wave velocity [PWV]), diet quality, and the gut microbiota. Outcomes were assessed at the baseline and the end of each study period. Diet quality, measured by the Healthy Eating Index-2015 (HEI-2015), was assessed using dietary data collected with the Automated Self-Administered 24-recall system (ASA24). Fecal samples from study completers were analyzed using 16S rRNA sequencing to assess gut microbiota composition and diversity. Sixty-six adults with prediabetes (40.9% female; [mean ± standard deviation]; age: 50.9 ± 11.6 years; BMI: 31.2 ± 4.0 kg/m2; FPG: 106.2 ± 6.4 mg/dL) at screening were randomized. Fifty-one adults completed the study. There were no significant between-condition mean differences for FPG (pistachio vs. usual care: 1.0 mg/dL [95% CI: -0.7, 2.9 mg/dL]). Insulin was higher after the pistachio condition versus usual care (3.0 µIU/mL [95% CI: 1.2, 4.8 µIU/mL]). HOMA-IR was higher after pistachio versus usual care (0.8 [95% CI: 0.3, 1.3]). PWV was lower after pistachios compared to usual care (-0.3 m/s [95%CI: -0.5, -0.0]). There were no between-condition mean differences for HbA1c, anthropometrics (weight, BMI, WC), lipid/lipoproteins, brachial BP, and central BP. The total HEI-2015 score was higher after the pistachio condition compared to usual care (5.6 points (95% CI: 0.2, 11.5]). Differences in total HEI scores were primarily driven by higher component scores for Seafood and Plant Protein (1.8 points [95% CI: 0.8, 2.8]) and Refined Grains (2.4 points [95% CI: 1.2, 3.6]) with pistachios. The pistachio condition resulted in higher consumption of total fat (3.9% kcals [95% CI: 0.2, 8.0]), monounsaturated fatty acids (2.2% kcals [95% CI: 0.4, 4.0]), fiber (5.0 g [95% CI: 1.1, 8.8]), potassium (487 mg [95% CI: 28, 946]), total protein (2.3 oz-eq [95% CI: 0.0, 4.6]), nuts and seeds (1.8 oz-eq [95% CI: 1.1, 2.6]), oils (12.2 g [95% CI: 1.4, 23.0]), and lower consumption of refined grains (1.5 oz-eq [95% CI: -2.8, -0.2]) versus usual care. Total energy intake was not different between conditions. There were no between condition mean differences in α- and β-microbial diversity. Following the pistachio condition, the bacteria genus Roseburia (Microbiome Multivariable Associations with Linear Models [MaAsLin] score = 2.1 ± 0.37 (SE); p = 0.00031) and NK4A214 group of Oscillospiraceae (MaAsLin score =1.0 ± 0.25; p = 0.045) were significantly enriched compared to the usual care condition. In adults with prediabetes, consuming 57 g of unsalted pistachios as a nighttime snack did not alter FPG compared to the usual care condition. The pistachio condition resulted in higher fasting insulin and HOMA-IR versus usual care. However, diet quality was improved during the pistachio condition. Also, intake of fiber, monounsaturated fatty acids, and total protein was increased. Butyrate-producing bacteria (Roseburia) increased after the pistachio condition, which is associated with gut health. A lactic acid bacteria associated with obesity (NK4A214 group of Oscillospiraceae) was also increased. Consuming pistachios as a nighttime snack compared to the usual care does not adversely affect FPG, increases insulin and insulin resistance, improves diet quality, and reduces arterial stiffness with beneficial changes to the gut microbiota. More research is needed determine the effect of nighttime pistachio consumption and the gut microbiota on glycemic in adults with prediabetes.